The Irish aviation authority, which is taking part in the official investigation into last weekend's Russian plane crash in Egypt, directed all Irish airlines on Wednesday not to fly to or from the Sinai Peninsula until further notice.
The Russian-operated Airbus A321 that came down on Saturday killing all 224 people on board was registered in Ireland and the Irish Aviation Authority has sent an expert to take part in the official investigation.
"The Irish Aviation Authority (IAA) directs Irish airline operators not to operate to/from Sharm elSheikh Airport, Egypt or in the Egyptian Sinai Peninsula airspace until further notice," the statement said.
An Egyptian source close to the investigation on Wednesday told Reuters the cause of Saturday's crash was looking more like an explosion but that it was not clear whether it was linked to a fuel or engine trouble or a bomb.
The crash was most likely caused by a bomb on the plane planted by ISIS or an ISIS affiliate. The official stressed that there has not been a formal conclusion reached by the U.S. intelligence community. "There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane," the official told CNN's Barbara Starr.
The assessment is not based on evidence obtained from the wreckage but from looking back at intelligence reports that had been gathered before Saturday's plane crash and intelligence gathered since then, CNN reported.
A bomb on board is one of three leading theories being discussed, as The Christian Science Monitor reported:
"It could have been a bomb," Paul Rogers, a global security consultant and professor at the University of Bradford in England, told the BBC. "The fact is that Russia recently intervened in Syria and … this could be a nasty blowback as far as [President Vladimir] Putin is concerned. The reality is that neither Egypt nor Russia will want to admit it involved terrorism and it may never come out fully."
(Reporting by Conor Humphries; Editing by Janet Lawrence and Gareth Jones)